The present invention relates to a water tank siphon operated water tank which can be controlled to discharge different volume of water for washing a lavatory bowl after night soil or urine.
In a flushing system, a water tank is provided to hold a fixed volume of water for washing a lavatory bowl each time after the discharge of night soil or urine by means of the control of a control knob or lever. After flushing, a water supply valve which is controlled by a float bowl is opened to let water flow into the water tank. Using this structure of water tank for washing a lavatory bowl is not economic because same volume of water has to be discharged for washing a lavatory bowl after the discharge of night soil as well as the discharge of urine. Since less amount of water is required for washing a lavatory bowl to use same volume of water for washing a lavatory bowl after the discharge of urine as what has been used in washing a lavatory bowl after the discharge of night soil.